1. Field of the Invention
The present invention relates to a method of manufacturing an organic electroluminescent device including organic electroluminescent elements.
2. Description of the Related Art
An organic electroluminescent device is one in which a plurality of organic electroluminescent elements are arranged on a substrate in a matrix pattern. A full-color image can be displayed using pixels each including a set of organic electroluminescent elements emitting, for example, red light, green light, and blue light.
Each organic electroluminescent element has a structure in which an organic compound layer with a thickness of about tens to hundreds of millimeters is placed between a pair of electrodes. The organic compound layer includes at least one light-emitting sub-layer. The color of light emitted from the organic electroluminescent element can be changed by appropriately selecting a luminescent material.
A vacuum vapor deposition method is widely used to form organic compound layers. In the case of forming layers each containing a luminescent material corresponding to an organic electroluminescent element by the vacuum vapor deposition method in the course of manufacturing a multicolor organic electroluminescent device, a layer containing a predetermined luminescent material is selectively formed on a predetermined region using a metal mask having openings corresponding to deposition regions. However, a vacuum vapor deposition method using a metal mask is unsuitable for the manufacture of a high-definition display because the accuracy of the alignment of the metal mask with a substrate for deposition is low due to the thermal expansion of the metal mask.
Japanese Patent No. 4507759 discloses a method in which an organic compound layer is selectively formed by photolithography with high accuracy without using a high-definition metal mask. In particular, the organic compound layer is formed over a substrate, an intermediate layer made of a water-soluble polymer and a photoresist layer are provided on the organic compound layer in that order, the photoresist layer and the intermediate layer are patterned by a known technique, and the organic compound layer is then patterned using the photoresist layer and the intermediate layer as a mask. After the organic compound layer is patterned, the intermediate layer is removed by dissolving the intermediate layer in water and the photoresist layer is also removed (lifted off) from the organic compound layer.
As described in Japanese Patent No. 4507759, the intermediate layer is placed between the organic compound layer and the photoresist layer for the purpose of reducing the damage caused to the organic compound layer by the application, exposure, and development of a photoresist. Since the intermediate layer is made of such a water-soluble material, the photoresist layer can be removed by dissolving the intermediate layer in water and therefore the organic compound layer is not damaged.
However, after the photoresist layer is removed by dissolving the intermediate layer, pieces of the lifted-off photoresist layer damage a surface of the organic compound layer remaining on the substrate because the photoresist layer is insoluble in water. This causes luminescent defects in some cases. Furthermore, it is difficult to completely remove the water-soluble polymer from the organic compound layer by dissolving the water-soluble polymer and therefore the water-soluble polymer, which is insulating, remains on a surface or interface of the organic compound layer. This may possibly cause the increase in driving voltage of an organic electroluminescent element.